The low frequency cardiac rhythm (LFCR) is an innovative, but underutilized, biological marker. The PI's studies show that LFCR is strongly associated with the state of cognitive persistence in controls. Cognitive persistence refers to the ability to remain on-task and inhibit impulsive off-task behavior. Additional preliminary data also suggest that children with Attention Deficit Hyperactivity Disorder (ADHD) may have differences in LFCR during cognitive tasks. A testable biological model of angiotensin activity is proposed to explain the empirically observed correlation between LFCR and cognitive functioning. Three impediments prevent the more extensive inclusion of LFCR in research studies. First, the methodology is too complex and time-consuming for most researchers. Second, the biological basis of LFCR is inadequately understood. Third, the psychometric properties of LFCR have not been fully characterized. BioAssessments will develop a turnkey biological/assessment system that integrates biological monitoring and cognitive assessment to solve these three impediments. The goals of Phase I are to remove these three impediments to using LFCR in research. To address the first impediment, a prototype will be built that permits nonspecialists to readily monitor LFCR. To address the second impediment, two additional biological measures will be used to confirm the biological basis of LFCR: blood assays of angiotensin and Transcranial Doppler sonography (TCD). To address the third impediment, 40 elementary school children will be simultaneously monitored (LFCR, blood assays, TCD) while performing two cognitive tasks. These data will be used to characterize the psychometric properties of LFCR. The PI has demonstrated the feasibility of this concept in three prior projects with children and adults. The Phase I product will make LFCR measurements more accessible to researchers and better grounded in a biological mechanism. In Phase II, the clinical utility of the proposed product will be validated at several additional research sites. The proposed product has the potential to address a pressing clinical need for better ADHD assessment tools. In Phase III, the turnkey system would be marketed to researchers who do not have specialized psychophysiological expertise. Long-term commercial applications may include the clinical assessment of ADHD. [unreadable] [unreadable]